refactor(document): switch collections to LAZY + add @EntityGraph + @BatchSize

- receivers, tags, trainingLabels: FetchType.EAGER → FetchType.LAZY
- sender: add explicit FetchType.LAZY (was implicitly lazy, now explicit)
- @NamedEntityGraph("Document.full"): sender + receivers + tags
- @NamedEntityGraph("Document.list"): sender + tags
- DocumentRepository.findById overridden with @EntityGraph("Document.full")
- DocumentRepository.findAll(Specification, Pageable) overridden with
  @EntityGraph("Document.list")
- DocumentRepository.findAll(Specification) overridden with
  @EntityGraph("Document.list") for RECEIVER/SENDER sort paths
- @BatchSize(50) on receivers and tags as fallback for any list path
  that does not go through an @EntityGraph method

Fixes issue #467.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/document/Document.java

@@ -2,6 +2,7 @@ package org.raddatz.familienarchiv.document;
 
 import jakarta.persistence.*;
 import lombok.*;
+import org.hibernate.annotations.BatchSize;
 import org.hibernate.annotations.CreationTimestamp;
 import org.hibernate.annotations.UpdateTimestamp;
 
@@ -21,6 +22,15 @@ import java.util.HashSet;
 import java.util.Set;
 import java.util.UUID;
 
+@NamedEntityGraph(name = "Document.full", attributeNodes = {
+        @NamedAttributeNode("sender"),
+        @NamedAttributeNode("receivers"),
+        @NamedAttributeNode("tags")
+})
+@NamedEntityGraph(name = "Document.list", attributeNodes = {
+        @NamedAttributeNode("sender"),
+        @NamedAttributeNode("tags")
+})
 @Entity
 @Table(name = "documents")
 @Data // Lombok: Generiert Getter, Setter, ToString, etc.
@@ -118,21 +128,23 @@ public class Document {
     @Builder.Default
     private ScriptType scriptType = ScriptType.UNKNOWN;
 
-    @ManyToMany(fetch = FetchType.EAGER)
+    @ManyToMany(fetch = FetchType.LAZY)
     @JoinTable(name = "document_receivers", joinColumns = @JoinColumn(name = "document_id"), inverseJoinColumns = @JoinColumn(name = "person_id"))
+    @BatchSize(size = 50)
     @Builder.Default
     private Set<Person> receivers = new HashSet<>();
 
-    @ManyToOne
+    @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "sender_id")
     private Person sender;
 
-    @ManyToMany(fetch = FetchType.EAGER)
+    @ManyToMany(fetch = FetchType.LAZY)
     @JoinTable(name = "document_tags", joinColumns = @JoinColumn(name = "document_id"), inverseJoinColumns = @JoinColumn(name = "tag_id"))
+    @BatchSize(size = 50)
     @Builder.Default
     private Set<Tag> tags = new HashSet<>();
 
-    @ElementCollection(fetch = FetchType.EAGER)
+    @ElementCollection(fetch = FetchType.LAZY)
     @CollectionTable(name = "document_training_labels", joinColumns = @JoinColumn(name = "document_id"))
     @Column(name = "label")
     @Enumerated(EnumType.STRING)

backend/src/main/java/org/raddatz/familienarchiv/document/DocumentRepository.java

@@ -7,6 +7,8 @@ import org.raddatz.familienarchiv.document.DocumentStatus;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.domain.Sort;
+import org.springframework.data.jpa.domain.Specification;
+import org.springframework.data.jpa.repository.EntityGraph;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.JpaSpecificationExecutor;
 import org.springframework.data.jpa.repository.Query;
@@ -23,6 +25,16 @@ import java.util.UUID;
 @Repository
 public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSpecificationExecutor<Document> {
 
+    @EntityGraph("Document.full")
+    Optional<Document> findById(UUID id);
+
+    @EntityGraph("Document.list")
+    Page<Document> findAll(Specification<Document> spec, Pageable pageable);
+
+    @EntityGraph("Document.list")
+    List<Document> findAll(Specification<Document> spec);
+
+
     // Findet ein Dokument anhand des ursprünglichen Dateinamens
     // Wichtig für den Abgleich beim Excel-Import & Datei-Upload
     Optional<Document> findByOriginalFilename(String originalFilename);